Money supply – also called money stock -- refers to the total amount of currency and other liquid financial products in an economy at a particular time. There are several measures of money supply, depending on which of the other non-currency products are included.M0, the narrowest definition of money supply, includes only hard currency in circulation. MB includes M0 plus hard currency held in bank reserves, which is not technically in circulation. M1, a very common definition of money supply, includes hard currency in circulation (M0), plus checking accounts, traveler’s checks, and certain other checkable deposits. Checking accounts, also called demand deposits, are moneys held in a bank, and therefore out of circulation, but the owner can retrieve them from the bank upon demand. M2 includes all of M1, plus savings deposits and CDs. Savings deposits and CDs are slightly less liquid than checking accounts, but can still be converted to cash quickly. M3 includes larger deposits, and MZM includes money market deposits. Economists study money supply and central banks manage the size of the money supply. When an economy is growing too slowly, carefully increasing money supply can stimulate it. When an economy is growing too quickly, decreasing money supply can slow down the economy and prevent inflation. Central banks control the money supply by raising and lowering their interest rates, which affects the rates charged by private banks. Higher rates decrease money supply. This management of the money supply through interest rates is called monetary policy.